On Fri, 22 Jun 2018, Kirill A. Shutemov wrote: > On Fri, Jun 22, 2018 at 02:05:47PM +0000, Thomas Gleixner wrote: > > On Tue, 12 Jun 2018, Kirill A. Shutemov wrote: > > > > > __pgtable_l5_enabled shouldn't be needed after system has booted, we can > > > mark it as __initdata, but it requires preparation. > > > > > > This patch moves early cpu initialization into a separate translation > > > unit. This limits effect of USE_EARLY_PGTABLE_L5 to less code. > > > > > > Without the change cpu_init() uses __pgtable_l5_enabled. cpu_init() is > > > not __init function and it leads to section mismatch. > > > > > > Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com> > > > Reviewed-by: Thomas Gleixner <t...@linutronix.de> > > > > Second thoughts. > > > > The only place where __pgtable_l5_enabled() is used in common.c is in > > early_identify_cpu() which is marked __init. So how is that section > > mismatch triggered? > > Yeah, it's not obvious: > > cpu_init() > load_mm_ldt() > ldt_slot_va() > LDT_BASE_ADDR > LDT_PGD_ENTRY > pgtable_l5_enabled()
How is that supposed to work correctly? start_kernel() .... trap_init() cpu_init() .... check_bugs() alternative_instructions() So the first invocation of cpu_init() on the boot CPU will then use static_cpu_has() which is not yet initialized proper. So, no. That does not work and the proper fix is: -unsigned int __pgtable_l5_enabled __initdata; +unsigned int __pgtable_l5_enabled __ro_after_init; and make cpu/common.c use the early variant. The extra 4 bytes storage are not a problem and cpu_init() is not a fast path at all. Thanks, tglx